1. Field of the Invention
This invention relates to electronic engine control.
2. Prior Art
Various means for controlling engines electronically are known. For example, U.S. Pat. No. 3,969,614 issued to Moyer et al teaches a method and apparatus for engine control. Adjustments to controlling the energy conversion function of an engine are obtained by sensing at least one engine operating condition, developing an electrical signal indicative of such condition, and, with a digital computer, calculating repetitively values corresponding to settings of the means used to control the energy conversion function of the engine. The digital computer is programmed to calculate these values or settings arithmetically from an algebraic function or functions describing a desired relationship between settings of the energy conversion control means and the sensed condition.
Typical control variables include the throttle angle, fuel flow per cycle, fuel injection timing, ignition timing, and, if EGR is used, the amount of exhaust gases recirculated through the engine. To effect control of these variables that determine the characteristics of the energy conversion process, various engine conditions may be sensed while the engine is operative. Thus, one or more of the following variable engine conditions may be sensed: crankshaft position, engine speed, mass airflow into the engine, intake manifold pressure, throttle angle, EGR valve position, throttle angle rate of change, engine speed rate of change, fuel temperature, fuel pressure, EGR valve rate of change, vehicle speed and acceleration, engine coolant temperature, engine torque, air to fuel ratio, exhaust emissions, etc.
It has been found that there are conditions when it is advantageous to operate with a very lean air fuel ratio. For example, such operation may produce better fuel economy or reduce exhaust emissions. Known engine control systems have difficulty operating the engine at or near the limit of lean air fuel ratios. It would be desirable to find an engine control system that easily and reliably is able to control engine operation at lean air fuel ratios. These are some of the problems this invention overcomes.